I went and looked at the past ten doping cases. Six of the past ten people popped for doping are Masters runners. They are:
Semaj Street
Michael Hooker
Shady Biwott
Loretta Turney
Cary Cooper
Robert Qualls
One is a junior Olympic competitor who was apparently given testosterone by his father. Another was a paralympic competitor (David Prince).
It's interesting that most of the doping that USADA is catching is happening in the more amateur areas of the sport. I've long thought that the 15 minute decline in BQ times couldn't be explained by shoe tech alone, and that doping had to be a factor in a drastic decline in times. Given that almost no hobby joggers are tested (they're catching the dopers who show up to USATF Masters Championships) out of competition and given just how many Masters runners they've caught lately, I really think that the vastness of the doping problem in the hobby jogger community is understated.